Total Aerodynamic Force

Cambered Airfoil in Positive Lift

Drag Types of Drag Induced: Caused by the Production of Lift Parasite: All Drag Not Caused by Lift Profile: Parasitic Drag of Rotor Blades Passing Through the Air

Drag Equation

D 2 V 2 SC D1

Largest Contributor to Total Drag

Low Speed: Induced Drag High Speed: Parasite/Profile Drag

Aerodynamics

Helicopter Drag vs. Airspeed

Aerodynamics

Airflow At A Hover - OGE

Aerodynamics

Airflow At A Hover - IGE

Aerodynamics

Translating Tendency Tendency of Aircraft to Drift In the Direction of Tail Rotor Thrust at a Hover

Compensated for by Mixing Unit & Pilot Input

Aerodynamics

10

Dissymmetry of Lift Difference in Lift Associated with the Advancing & Retreating Sides of the Rotor System

Compensated for by Blade Flapping & Cyclic Feathering

Aerodynamics

11

Blade Flapping Up/Down Movement of the Rotor Blade About A Flapping Hinge

Causes Blowback (Rearward Tilt of Rotor Disk)

Aerodynamics

12

Blade Lead & Lag (Hunting)

Fore & Aft Movement of the Blade in Tip Path Plane Due to Changes in Blade Speed

Coriolis EffectAngular Velocity Changes with Blade CG

Aerodynamics

13

Retreating Blade Stall

Outboard Section of Retreating Blade Stalls at High Forward Airspeed

CausesBlade Flapping & Cyclic Feathering that Exceed Critical Angle

Aircraft Pitches Up & Rolls Left

Conditions Conducive to Retreating Blade Stall

- High GWT - High DA - Turbulent AirAerodynamics

- Low Rotor RPM - High G Maneuvers

14

Retreating Blade Stall

Aerodynamics

15

Compressibility Outboard Section of Advancing Blade Exceeds the Speed of Sound at High Airspeed

Aerodynamic Center Moves Aft

Large Down Pitching Moment at Outboard Tip Will Cause Structural Failure of Blade

Aircraft Pitches Down Conditions Conducive to Compressibility

- High Airspeed - High GWT - Low TemperatureAerodynamics

- High Rotor RPM - High DA - Turbulent Air

16

Settling with Power

(Vortex Ring State) Formation of an Inner Vortex on the Blade Causes Substantial Loss of Lift Increased Collective Results in Larger Vortex Rings & Higher Rates of Descent Conditions Conducive to Settling with Power Very Low Forward Airspeed 20-100% of Available Power Applied 300 ft/min Rate of Descent or Greater

Recover by Establishing Directional Flight

Aerodynamics

17

Vortex Ring State

Induced Flow Before Vortex Ring State

Vortex Ring State

Aerodynamics

18

Offset Hinges

Tends to Align the Helicopter with the Rotor Tip Path Plane Offset Creates a Hub MomentLarger the Offset, Higher the Hub Moment